It's hard to say for certain because of the limited amount of information that you've provided, but I think that the problem that you're going to be faced with when trying to use any of the existing previewer code is one of authentication. If you're using only using CMIS then you won't be able to use any of the WebScript based REST APIs that the Alfresco widgets will be using.
There are two possible previewer widgets that you can use - the older YUI2 based previewer (that you'd currently find in the document details page and the Document Library film strip view, and the newer Aikau component that you'd find in the faceted search previewer (from version 5.0 onwards).
I suspect that you won't be able to re-use either of these components without either authenticating against Alfresco in a way that allows you to access the WebScript based REST APIs or extending and customizing those widgets.
You've said that you have your own Spring MVC application, but you haven't said whether or not that is using the Surf extension - if it is, and you're using the authentication capabilities provided by Surf then you will be authenticated to use those REST APIs - as the Surf authentication provides access across all APIs (including CMIS) via a single authentication.
If you are able to access those APIs then you should be able to follow the steps outlined in both the form post and the blog posts in your own question and the previous answer, however - based on your question I suspect that you can't do that.
If you've not come across it, you might be interested in the Aikau archetype that builds a ready-made Alfresco client using Surf (see this link) and that tutorial also shows how to use the Aikau previewer (see here).
Because this is providing you with a Spring MVC client that is preconfigured to authenticate against Alfresco, you might be able to port your application to use it.
Otherwise, as I said earlier - chances are you'll need to extend the existing widgets to use the CMIS APIs to render the previewers. Again, Aikau is easier to extend that the old YUI2 widgets - but is reliant on Surf.
